The effect of prenatal irradiation on the postnatal tumor response of mice will be studied. Female C57B1 mice bred to C3H males will be exposed to 0, 10 or 50 rad of and 17. One group of offspring will be treated with phorobol myristate acetate (PMA) beginning at weaning to determine if cell were initiated by the radiation and can be promoted to develop tumors. Another group will be treated neonatally with urethan and the tumor response compared with mice receiving no postnatal treatment. This will be used to evaluate sensitivity to a postnatal carcinogenic stimulus is altered by prenatal irradiation. Finally, remaining animals from these prenatally treated groups will be tested for the responsiveness to transplanted tumors to determine if tumor cells are better able to grow in animals prenatally irradiated.